<!DOCTYPE html>
<html>

	<head>
		<meta charset="UTF-8">
		<title></title>
	</head>
	<body>
	</body>
	<script>
		setTimeout(function() {
			var b = "big";
			callback(b);
		}, 2000);
		var callback = function(b) {
			alert(b);
		}
	</script>

</html>